Downward pumping of magnetic flux as the cause of filamentary structures in sunspot penumbrae

Thomas, John H.; Weiss, N. O.; Tobias, Steven M.; Brummell, Nicholas H.

doi:10.1038/nature01174

Cited by 109 publications

(110 citation statements)

References 19 publications

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“…This field may remain below the solar surface until well outside the sunspot, as proposed by Thomas et al (2002). It may also form a structure similar to a -loop, returning to the surface within the penumbra ) and possibly moving outwards (Sainz Dalda & Bellot Rubio 2008), appearing as a pair of moving magnetic features outside the penumbra, as proposed by Zhang et al (2003).…”

Section: Structure Of Penumbral Filamentsmentioning

confidence: 81%

Structure of sunspot penumbral filaments: a remarkable uniformity of properties

Tiwari

Noort

Lagg

et al. 2013

A&A

204

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Context. The sunspot penumbra comprises numerous thin, radially elongated filaments that are central for heat transport within the penumbra, but whose structure is still not clear. Aims. We aim to investigate the fine-scale structure of these penumbral filaments. Methods. We perform a depth-dependent inversion of spectropolarimetric data of a sunspot very close to solar disk center obtained by Solar Optical Telescope/Spectropolarimeter onboard the Hinode spacecraft. We have used a recently developed, spatially coupled 2D inversion scheme, which allows us to analyze the fine structure of individual penumbral filaments up to the diffraction limit of the telescope.Results. Filaments of different sizes in all parts of the penumbra display very similar magnetic field strengths, inclinations, and velocity patterns. The temperature structure is also similar, although the filaments in the inner penumbra have cooler tails than those in the outer penumbra. The similarities allowed us to average all these filaments and to subsequently extract the physical properties common to all of them. This average filament shows upflows associated with an upward-pointing field at its inner, umbral end (head) and along its axis, as well as downflows along the lateral edge and strong downflows in the outer end (tail) associated with a nearly vertical, strong, and downward-pointing field. The upflowing plasma is significantly, i.e., up to 800 K, hotter than the downflowing plasma. The hot, tear-shaped head of the averaged filament can be associated with a penumbral grain. The central part of the filament shows nearly horizontal fields with strengths in the range of 1 kG. The field above the filament converges, whereas a diverging trend is seen in the deepest layers near the head of the filament. The fluctuations in the physical parameters along and across the filament increase rapidly with depth. Conclusions. We put forward a unified observational picture of a sunspot penumbral filament. It is consistent with such a filament being a magneto-convective cell, in line with recent magnetohydrodynamic simulations. The uniformity of its properties over the penumbra sets constraints on penumbral models and simulations. The complex and inhomogeneous structure of the filament provides a natural explanation for a number of long-running controversies in the literature.

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Section: Structure Of Penumbral Filamentsmentioning

confidence: 81%

Structure of sunspot penumbral filaments: a remarkable uniformity of properties

Tiwari

Noort

Lagg

et al. 2013

A&A

204

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“…The convective flows are able to drive the field lines downwards and submerge some of the penumbral flux below the photosphere (Thomas et al, 2002). This leads to a variation in inclination of the penumbral filaments and produces an interlocking comb structure (Thomas and Weiss, 1992).…”

Section: Main Laws and Intrinsic Characteristics Of Large-scale Magnementioning

confidence: 99%

Evolution of Active Regions

Driel-Gesztelyi

Green

2015

Living Rev. Sol. Phys.

237

129

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The evolution of active regions (AR) from their emergence through their long decay process is of fundamental importance in solar physics. Since large-scale flux is generated by the deepseated dynamo, the observed characteristics of flux emergence and that of the subsequent decay provide vital clues as well as boundary conditions for dynamo models. Throughout their evolution, ARs are centres of magnetic activity, with the level and type of activity phenomena being dependent on the evolutionary stage of the AR. As new flux emerges into a pre-existing magnetic environment, its evolution leads to re-configuration of small-and large-scale magnetic connectivities. The decay process of ARs spreads the once-concentrated magnetic flux over an ever-increasing area. Though most of the flux disappears through small-scale cancellation processes, it is the remnant of large-scale AR fields that is able to reverse the polarity of the poles and build up new polar fields. In this Living Review the emphasis is put on what we have learned from observations, which is put in the context of modelling and simulation efforts when interpreting them. For another, modelling-focused Living Review on the sub-surface evolution and emergence of magnetic flux see Fan (2009). In this first version we focus on the evolution of dominantly bipolar ARs. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

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“…Thomas et al (2002) report on strong, coherent, descending plumes resulting from turbulent, compressible convection at the outer edge of a simulated sunspot. In the most recent magneto-hydrodynamic (MHD) simulations (Rempel 2012), the average velocity in the supersonic downflow regions is found to be 9.6 km s −1 at optical depth unity, with the fastest flows in the outer regions of the penumbra reaching up to 15 km s −1 .…”

Section: Introductionmentioning

confidence: 99%

Peripheral downflows in sunspot penumbrae

Noort

Lagg

Tiwari

et al. 2013

A&A

127

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Context. Sunspot penumbrae show high-velocity patches along the periphery. Aims. The high-velocity downflow patches are believed to be the return channels of the Evershed flow. We aim to investigate their structure in detail using Hinode SOT/SP observations. Methods. We employ Fourier interpolation in combination with spatially coupled height dependent LTE inversions of Stokes profiles to produce high-resolution, height-dependent maps of atmospheric parameters of these downflows and investigate their properties. Results. High-speed downflows are observed over a wide range of viewing angles. They have supersonic line-of-sight velocities, some in excess of 20 km s −1 , and very high magnetic field strengths, reaching values of over 7 kG. A relation between the downflow velocities and the magnetic field strength is found, in good agreement with MHD simulations. Conclusions. The coupled inversion at high resolution allows for the accurate determination of small-scale structures. The recovered atmospheric structure indicates that regions with very high downflow velocities contain some of the strongest magnetic fields that have ever been measured on the Sun.

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Downward pumping of magnetic flux as the cause of filamentary structures in sunspot penumbrae

Cited by 109 publications

References 19 publications

Structure of sunspot penumbral filaments: a remarkable uniformity of properties

Structure of sunspot penumbral filaments: a remarkable uniformity of properties

Evolution of Active Regions

Peripheral downflows in sunspot penumbrae

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